Sabikui Bisco

In the far future, a disaster known as the “Rusty Wind” has transformed the majority of Japan into a barren desert and left civilization in tatters. After his teacher falls prey to the rust, the roguish Bisco Akahoshi embarks on journey through the sandy wastes to obtain a mushroom known only as the Rust Eater, rumored to cure the ailment. Together with the dashing young doctor Milo, the pair will have to contend with the unforgiving environment and their fellow wanderers in order to make it back alive.
(Source: Yen Press)
Note: Sabikui Bisco won Silver Prize in the 2017 Dengeki Novel Prize, and placed first in the Kono Light Novel ga Sugoi! ranking in the best light novel category in 2019.